Method for reducing exhaust noxious emission of rotary engine and the system therefor

ABSTRACT

Method and system for reducing unburned and partially burned noxious gases inevitably contained in engine exhaust gases of a rotary engine having an exhaust gas cleaner in its exhaust system. In the method and system, a fresh air-fuel mixture existing in the engine chamber is periodically introduced into the exhaust system directly into or upstream of the exhaust gas cleaner in response to the compression condition of the engine chamber, thus improving the afterburning condition of the exhaust gas cleaner through warming-up. For this purpose, an enriched mixture left behind in a trailing portion of the engine chamber may exclusively be drawn into the cleaner so as to uniformalize the mixture ratio distribution in the whole engine chamber. Furthermore, the mixture may be shut off when the operating temperature of the cleaner is above a predetermined level dictating that the warming-up thereof is completed.

United States Patent '0 14G 22G V 2 PIPE "'L R VA To TAIL 22 Yamamoto 11 Feb. 12, 1974 1 1 METHOD FOR REDUC1NG EXHAUST 3,451,213 6/1969 Lang/294 NOXIOUS EMISSION OF ROTARY ENGINE i l i g 284 a a as i 286 AND THESYSTEM THEREFOR 3,662,540 5/1972 Murphey 60/274 Inventor: KenichiYamamoto, Hiroshima,

Japan Primary Examiner'Douglas Hart [73] Assignee: Toyo Kogyo Co., Ltd.,Aki-gun,

Hiroshama-ken, Japan 1 [57] ABSTRACT [22] Fil d; M r, 8, 1972 Method andsystem for reducing unburned and partially burned noxious gasesinevitably contained in en- [21] Appl' 232671 gine exhaust gases of arotary engine having an exhaust gas cleaner in its exhaust system. inthe method [30] Foreign Ap li ti P i it D t and system, a fresh air-fuelmixture existing in the en- Mar. 10 1971 Japan 46-13231 gine Chamber isPeriodically introduced the May 8 1971 Japan 46-40445 haust systemdirectly into or upstream of the exhaust gas cleaner in response to thecompression condition 52 us. Cl 60/286 60/294 60/901 engine chamber,thus-Proving aflerbum- {23/801 123/182 ing condition of the exhaust gascleaner through 51 Int. Cl. 1 62b 75/10 warming-P this Purim, anenriched mixlure of Search 13ft 111 a trailing P0111011 Of the enginechamber 123/182 may exclusively be drawn into the cleaner so as to uniformalize the mixture ratio distribution in the whole [56] ReferencesCited engine chamber. Furthermore, the mixture may be shut off when theoperating temperature of the UNITED STATES PATENTS cleaner is above apredetermined level dictating that 3,228,185 1/1966 Bergstrom 60/289 thewarmingmp thereof is completed 3,270,719 9/1966 Hamada 123/182 3,446,1905/1969 Bensinger 123/801 19 Claims, 3 Drawing Figures 1 METHOD FORREDUCING EXHAUST NOXIOUS EMISSION OF ROTARY ENGINE AND THE SYSTEMTHEREFOR BACKGROUND OF THE INVENTION The present invention relatesgenerally to an internal combustion engine of rotary type, and moreparticularly to a system for reducing unburned and partially burnednoxious gases inevitably contained in engine exhaust gases of suchrotaty engine as having an exhaust gas cleaner in its exhaust system.

The presence of unburned and partially burned noxport an exhaust gascleaner, such as, an after-bumer or a chemical converter using acatalyst, in which the contaminated exhaust gases containinghydrocarbons and- ]or carbon monoxide are to be reburned in the presenceof fresh air or some suitable oxidizer.

Difficulties have, however, been encountered by the prior art methods ineffectively reducing the noxious gases during a certain mode ofautomobile operation. Immediately after an internal combustion engine isinitially started, the exhaust gas cleaner is kept cold for a while,with its deteriorated reburning ability. Thus, during the idle operationof the engine until it is sufficiently warmed up, the exhaust gascleaner does not restore its high reburning ability, leaving aconsiderable amount of such air pollutants to issue from the exhausttail pipe.

Apart from the above difficulties common to any type of internalcombustion engine, there is also a serious problem inherent, to a rotaryengine. As is well known in the art, on intake and compression strokesof a rotary engine an air-fuel mixture is locally enriched especially inthe neighbourhood of the trailing portion of the engine chamber. This'ispartly because fuel droplets, if any, of relatively large size tend tobe left behind in the course of the intake and compression strokes dueto their inertial properties, and partly because the sealing membersmounted on the lobes of the rotor are apt to sweep off, as the rotorrotates in its regular sequence, the liquid fuel layer deposited on theinner surface of the engine center housing. When, as a result, theair-fuel mixture as a whole is ignited near the termination of thecompression stroke, namely, immediately anteriorly to the T.D.C. (topdead center) point, a locally irregular combustion is accomplished inthe engine combustion chamber, thus producing a quantity of reactionintermediates such as hydrocarbons or carbon monoxide. This unfavourablecombustion phenomenon is found dominant especially during the idle orwarming-up operation of the rotary engine when the engine temperatureremains lowered and when the cleaning ability of the exhaust gas cleanerremains deteriorated. In the long run, the major cause for which it ispractically impossible to minimize the noxious gas content in theexhaust gases of a rotary engine even with an exhaust gas cleaner isthat the leading and trailing portions of the engine chamber undercompressioncontain air-fuel mixtures of different mixture ratios.

SUMMARY OF THE INVENTION According to a primary aspect of the presentinvention, a fresh air-fuel mixture existing in an engine chamber undercompression of a rotary engine having an exhaust gas cleaner in itsexhaust system is periodically introduced into the exhaust systemdirectly into or upstream of the exhaust gas cleaner in response to thecompression condition of the engine chamber so that theafterburningcondition of the exhaust gas cleaner may be improved throughwarming-up by the fresh airfuel mixture introduced.

According to anotherimportant aspect of the invention, the periodicintroduction of the fresh air-fuel mixture is eHected by drawing anenriched fresh air-fuel mixtureleft behind in a trailing portion of theengine chamber so that the distribution of the mixture ratio in thewhole engine chamber may be uniformalized.

According to a further important aspect of the invention, the periodicintroduction of the fresh air-fuel mixture is shut off when theoperating temperature of the exhaust gas cleaner is above apredetermined level dictating that the warming-up thereof is completed.

It is therefore an object of the present invention to provide animproved method and system for use with an internal combustion engine ofrotary type having an exhaust gas cleaner in' its exhaust system, whichmethod and system implement the above aspects for reducing unburned andpartially burned noxious gases inevitably contained in the engineexhaust gases.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION or THE PREFERREDEMBODIMENTS Referring now to FIG. 1, an exhaust noxious emissionreducing system according to the present invention is generallydesignated at numeral l0'and is used in combination with an internalcombustion engine 11. This rotary engine 1 1 may be any conventionaltype and will be of rotary type described, by way of example, to includean engine housing composed of an annular center housing 12 having atrochoidal inner peripheral wall 13 and side walls (not shown), bothdefining an engine chamber 14. A generally trigonal rotor or rotarypiston 15 is eccentrically rotatably mounted about a crankshaft (notshown) within the engine chamber 14. This rotor 15 is provided at itsrespective apex 15a and flank 15b with suitable sealing members (notshown), thus establishing fluid tight seal between the rotor 15 andinner wall 13. As the rotor rotates about the crankshaft in thedirection of an arrow 16, four strokes are carried out in the regularsequence of intake, compression, explosion and exhaust. .For effectingthese strokes, an intake port 17 is formed, as shown, in the enginehousing and operates to admit a fresh air-fuel mixture usually properlyatomized into the combustion zone of the engine chamber 14. In theengine housing, is also formed an exhaust port 18 for expelling theburned gases from the engine chamber 14. A suitable ignition means 19,which is shown two in number, is also mounted in the engine housing forigniting the air-fuel mixture in the combustion zone. In order toafterbum or consume the unburned or partially burned noxious gases, therotary engine 1 1 of shown type is provided with an exhaust gas cleaner21 which is usually located in an exhaust system (not numbered)downstream of the exhaust port 18. This exhaust gas cleaner 21 may be ofany type, such as, an after-burner or a chemical converter using acatalyst, in which the contaminated exhaust gases are to be consumed inthe presence of air or some kind of oxidizer.

The system of the invention generally includes a bypass conduit 22 andsuitable control means 23, as shown. The bypass conduit 22 is providedat its both ends with an inlet port 22a open into the engine chamber 14and with an outlet port 22b open into the exhaust port 18, asillustrated, or directly into the exhaust gas cleaner 21. The inlet port22a is, more specifically, located in a portion of the engine housingwhich defines an engine chamber under compression. However, the inletport 22a preferably is located in the engine chamber under intake whenthe rotor 15 is in a rotational position which is depicted by the solidline, indicating that the combustible air-fuel mixture is about to beignited. It is easily understood that the inlet port 22a may be formedin either of the side walls at the rotationally corresponding positionthereof. In any event, the inlet port 22a is designed to open at leastinto an engine chamber under compression 14a.

Turning to FIG. 3, the position of the rotor 15 depicted by the solidline. corresponds in a compression pressure curve, as illustrated as asolid line 31a and a dotted line 31b, to a point A indicative ofthese-called T.D.C. (top dead center) point. As is well known, thisT.D.C. point implies that the crank angle is zero degree with the.highest compressure pressure. Another point B riding on the solid curve31a thus indicates that the compression pressure is slightly lower thanthat miximum, in other words, that the crank angle as located by anotherpoint C is immediately anterior to the T.D.C. point. After ignition, thechamber pressure abruptly increases on a characteristic curve 32, asshown in FIG. 3.

Reverting now to FIG. 1, the control means 23 is mounted midway of thebypass 22 and responds to the compression condition of the enginechamber 14a in terms directly of the compression pressure therein or ofthe crank angle so that it can permit periodic introduction of thecompressed air-fuel mixture by way of the bypass conduit 22 into theexhaust gas cleaner 21. The control means 23 may be of any prior artvalve which is preset to open when the rotor 15 assumes the rotationalposition as shown by the dotted line. This rotational position isdictated by the particular point B in terms of the chamber pressure orby the specific point C in terms of the crank angle.

The control means 23 may be a pressure relief valve which is directlyresponsive to the compression pressure in the engine chamber undercompression 14a. A solenoid valve may also be employed as the controlmeans 23 and is adapted to open when energized. In

this instance, a crank angle sensor (not shown) is used for supplying anelectric signal to the solenoid valve so as to energize the same whenthe crank angle reaches the level of C Just anterior to the T.D.C.point. Furthermore, the control means 23 may preferably include a usualmechanical valve adapted to open when actuated, and a mechanical linkage(not shown) associated with the rotation of the rotor 15 for actuatingthe mechanical valve when the crank angle reaches the level of C. Thesemeans for controlling the control means 23 as a function of the sensedcrank angle are shown generally by block 30 (FIG. 1).

When, in operation, a fresh air-fuel mixture is sucked into the enginechamber 14 through the intake port 17, the air-fuel mixture is thencompressed therein as the rotor 14 rotates on the compression strokeuntil it assumes the rotational position of the solid line, as shown.Meanwhile, the control valve 23 opens at the moment when the rotor 15passes the position of the dotted line. With this valve 23 open, acalibrated amount of air-fuel mixture is drawn or expelled through thebypass conduit 22 into the exhaust port 18 and immediately later intothe exhaust gas cleaner 21 for afterburning. It should be appreciatedhere that with the inlet port 22a located in the trailing portion of theengine housing defining the chamber under compression, a locallyenriched portion of air-fuel mixture can be introduced into the exhaustgas cleaner 21. This advantage will be reflected by the fact that thedistribution of the mixture ratio is accordingly uniformalized in theengine combustion chamber, with the resultant regular combustionproducing less unburned and partially burned content in the engineexhaust gases.

As is most experienced in the idle and high acceleration of theautomobile operation, the air-fuel mixture expelled from the trailingportion of the chamber under compression is of over-rich nature so thatit is quite desirable to supply secondary air before the mixture entersthe exhaust gas cleaner 21. In this way, a sufficient amount of freshand still non-contaminated air is supplied into the cleaner 21 so as toimprove the combustion condition of the same. In other words, thecleaner 21 can be properly preheated or warmed up within shortened timeperiod.

In order to effect the introduction of the fresh secondary air, asecondary air means is provided, including a secondary air conduit 24having an outlet port 24a open into the exhaust port 18 in the vicinityof the outlet port 22b of the bypass conduit 22. An air pump 25 maypreferably be provided to have fluid communication with the secondaryair conduit 24 for pumping out therethrough secondary fresh air having apressure level higher than exhaust back pressure which may probablyobtain in the exhaust port 18. It is also preferred that theintroduction of the secondary air is performed in a manner tosufficiently admix the secondary air with the engine exhaust gasescontaining the fresh air-fuel mixture. Between the secondary air conduit24 and air pump 25 is desirably mounted an air container 26 fortemporarily storing the secondary air before its introduction into theexhaust port 18.

With these in mind, although the heating of the exhaust gas cleaner 21during the idle or warming-up operation is promoted by the embodiment ofthe present system of FIG. 1, there arises some drawback from theoperation of the control valve 23. That is, since the control valve 23opens and closes merely in response to the compression condition of theengine chamber 14 under compression, the air-fuel mixture continues tobe expelled on the compression stroke even after the exhaust gas cleaner21 is sufficiently warmed up to have a proper cleaning effect. Thisinevitably invites some degradation in fuel economy. and engineperformance.

.Thisdrawback can be removed by providing suitable shut-off meansreponsive to the operating temperature of the exhaust gas cleaner 21.More specifically, the introduction of the air-fuel mixture is shut offby the shutoff means when the operating temperature is above apredetermined level dictating that the warming-up of the cleaner 21 iscompleted.

Another embodiment implementing this concept will be described inconnection with FIG. 2, in which the operating temperature is senseddirectly at the cleaner 21. In more detail, a shut-off valve 27 ismounted midway of the bypass conduit 22 in series with the control valve23. This shut-off valve 27 is adapted to close tainer 26 are omittedbecause of the restricted space allowed for FIG. 2.

The warming-up sensor 28 may also include a me chanical element, forexample, a bimetal element or a thermal expansion element, which sensesthe operating temperature and which is mechanically linked with theshut-off valve 27 for its actuation. On the other hand, the warming-upsensor 28 may be located adjacent either to the engine housing 12 orexhaust port 18 for sensing the operating temperature respectively interms of the engine housing temperature or of the temperature of theexhaust gases. Regarding to the relative location of the control valve23 and shut-off valve 27, it will be understood that the former isupstream of the latter in the flow direction of the air-fuel mixture tobe bypassed, and vice versa.

' When the rotary engine 11 is initially started with the exhaust gascleaner 21 being cold, and the shut-off valve 27 remains open due to thefact that the temperature of the cleaner 21 is below the predeterminedlevel. Therefore, the control valve 23 is made to open, as has beenexplained with reference to FIG. 1, at the instant when the compressionpressure assumes a predetermined value corresponding to the point B or Cshown in FIG. 3. As a result, a locally enriched air-fuel mixture leftbehind in the trailing portion of the engine chamber under compression14a is drawn by way of the bypass conduit 22 into the exhaust port 18.This enriched mixture is then burned or reacted in the exhaust gascleaner 21 to preheat or warm up the same.

At the succeeding stage when the cleaner 21 is fully warmed up, theshut-off valve 27 is closed to prevent the airfuel mixture undercompression from spurting into the exhaust port 18. By this stage, thecombustion condition of the engine 11 has already been improved togetherwith its atomization performance. Thus, the 6 sucked by or mixed withthe intake mixture of the succeeding cycle. In this way, the previousdrawback of degradation in fuel economy and engine performance isremoved after the operating temperature of the cleaner 21 is higher thanthe predetermined level, even if there is no introduction of theair-fuel mixture thereinto.

As is apparent from the description hereinbefore made, the exhaustnoxious emission reducing system according to the invention can improvethe combustion condition of an exhaust gas cleaner used in an internalcombustion engine of rotary type. Therefore, the system can minimize theunburned and partially burned content in the engine exhaust gasesespecially during the idel or warming-up operation of the rotary engine,thus being conductive to a prominent solution for the serious airpollution problem.

What is claimed is:

l. A system for reducing unburned and partially burned gases containedin engine exhaust gases of an internal combustion engine of rotary typehaving an exhaust gas cleaner in its exhaust system, said systemcomprising:

a bypass conduit having an inlet port open into an engine chamber undercompression and an outlet port open into an exhaust system for providingfluid communication therebetween; and

control means responsive to the compression condition of said enginechamber for periodically permitting said fluid communication so as tointroduce by way of said bypass conduit into said exhaust gas cleaner afresh air-fuel mixture from said engine chamber, wherein said controlmeans includes a pressure relief valve mounted in said bypass conduitand responsive directly to the compression pressure in said enginechamber for effecting the periodical introduction of said fresh air-fuelmixture when said compression pressure is above a predetermined levellower than its maximum;

whereby thee unburned and partially burned gases are afterburned to aminimum in said exhaust gas cleaner. I

2. A system for reducing unburned and partially burned gases containedin engine exhaust gases of an internal combustion engine of rotary typehaving an exhaust gas cleaner in its exhaust system, said systemcomprising:

a bypass conduit having an inlet port open into an engine chamber undercompression and an outlet port open into an exhaust system for providingfluid communication therebetween; and

control means responsive to the compression condi tion of said enginechamber for periodically permitting said fluid communication so as tointroduce by wayof said bypass conduit into said exhaust gas cleaner afresh air-fuel mixture from said engine chamber, wherein said controlmeans includes valve means mounted in said bypass conduit and responsiveto the crank angle of said internal combustion engine for effecting theperiodical intro duction ofsaid fresh air-fuel mixture when said crankangle is below a predetermined level dictating anteriority to the T.D.C.point;

whereby the unburned and partially burned gases are afterburned to aminimum in said exhaust gas cleaner.

3. A system for reducing unburned and partially burned gases containedin engine exhaust gases of an internal combustion engine of rotary typehaving an exhaust gas cleaner in its exhaust system, said systemcomprising:

a bypass conduit having an inlet port open into an engine chamber undercompression and an outlet port open into an exhaust system for providingfluid communciation therebetween, wherein the inlet port of said bypassconduit is located in a trailing portion of an engine housing definingsaid engine chamber for admitting therethrough an enriched freshair-fuel mixture left behind in the trailing portion of said enginechamber; and

control means responsive to the compression condition of said enginechamber for periodically permitting said fluid communication so as tointroduce by way of said bypass conduit into said exhaust gas cleaner afresh air-fuel mixture from said engine chamber,

whereby the unburned and partially burned gases are afterburned to aminimum in said exhaust gas clean'er.

4. A system according to claim 2, further comprising shut-off meansresponsive to the operating temperature of said exhaust gas cleaner forshutting off the introduction of said fresh air-fuel mixture when saidoperating temperature is above a predetermined level dictating that thewarming-up of said exhaust gas cleaner is completed.

5. A system according to claim 2, wherein said valve means includes asolenoid valve adapted to open when energized, and a crank angle sensorsensing said crank angle for supplying an electric signal to saidsolenoid valve for its energization when said crank angle reaches saidpredetermined level.

6. A system according to claim 2, wherein said valve means includes amechanical valve adapted to open when actuated, and a mechanical linkageassociated with the rotation of the rotor of said internal combustionengine for actuating said mechanical valve when said crank angle reachessaid predetermined level.

7. A system according to claim 3, further comprising secondary air meansfor introducing fresh secondary air into said exhaust system upstream ofsaid exhaust gas cleaner in a manner to sufficiently admix said freshsecondary air with said engine exhaust gases containing said freshair-fuel mixture.

8. A system according to claim 7, wherein said secondary air meansincludes a secondary air conduit having an outlet port open into saidexhaust system in the vicinity of the outlet port of said bypassconduit, and an air pump having fluid communication with said secondaryair conduit for pumping out therethrough said fresh secondary airhavinga pressure level higher than a probable exhaust back pressure in theexhaust port of said internal combustion engine.

9. A system according to claim 8, wherein said secondary air meansfurther includes an air container mounted between said secondary airconduit and air pump for temporarily storing said fresh secondary airbefore its introduction.

10. A system according to claim 3, further comprising shut-off meansresponsive to the operating temperature of said exhaust gas cleaner forshutting off the introduction of said fresh air-fuel mixture when saidoperating temperature is above a predetermined level dictating that thewarming-up of said exhaust gas cleaner is completed.

11. A system according to claim 10, wherein said shut-off means includesa shut-off valve mounted said bypass conduit in series with said controlmeans and adapted to close when actuated, and a warming-up sensorsensing the operating temperature of said exhaust gas cleaner foractuating said shut-off valve when said operating temperature is abovesaid predetermined level.

12. A system according to claim 11, wherein said warming-up sensor islocated adjacent to an engine housing defining said engine chamber forsensing said operating temperature in terms of the temperature of saidengine housing.

13. A system according to claim 11, wherein said warming-up sensor islocated adjacent to said exhaust system for sensing said operatingtemperature in terms of the temperature of said engine exhaust gases.

14. A system according to claim 11, wherein said warming-up sensor islocated adjacent to said exhaust gas cleaner for sensing said operatingtemperature in terms of the temperature of said exhaust gas cleaner.

15. A system according to claim 11, wherein said warming-up sensorincludes a mechanical element mechanically linked with said shut-offvalve for its actuation.

16. A system according to claim 15, wherein said mechanical elementincludes a bimetal element for sensing said operating temperature.

17. A system according to claim 15, wherein said mechanical elementincludes a thermal expansion element for sensing said operatingtemperature.

18. A system according to claim 11, wherein said warming-up sensorincludes an electric element for supplying an electric signal to saidshut-off valve for its actuation.

19. A system according to claim 18, wherein said electric elementincludes a thermistor for sensing said operating temperature.

1. A system for reducing unburned and partially burned gases containedin engine exhaust gases of an internal combustion engine of rotary typehaving an exhaust gas cleaner in its exhaust system, said systemcomprising: a bypass conduit having an inlet port open into an enginechamber under compression and an outlet port open into an exhaust systemfor providing fluid communication therebetween; and control meansresponsive to the compression condition of said engine chamber forperiodically permitting said fluid communication so as to introduce byway of said bypass conduit into said exhaust gas cleaner a freshair-fuel mixture from said engine chamber, wherein said control meansincludes a pressure relief valve mounted in said bypass conduit andresponsive directly to the compression pressure in said engine chamberfor effecting the periodical introduction of said fresh air-fuel mixturewhen said compression pressure is above a predetermined level lower thanits maximum; whereby thee unburned and partially burned gases areafterburned to a minimum in said exhaust gas cleaner.
 2. A system forreducing unburned and partially burned gases contained in engine exhaustgases of an internal combustion engine of rotary type having an exhaustgas cleaner in its exhaust system, said system comprising: a bypassconduit having an inlet port open into an engine chamber undercompression and an outlet port open into an exhaust system for providingfluid communication therebetween; and control means responsive to thecompression condition of said engine chamber for periodically permittingsaid fluid communication so as to introduce by way of said bypassconduit into said exhaust gas cleaner a fresh air-fuel mixture from saidengine chamber, wherein said control means includes valve means mountedin said bypass conduit and responsive to the crank angle of saidinternal combustion engine for effecting the periodical introduction ofsaid fresh air-fuel mixture when said crank angle is below apredetermined level dictating anteriority to the T.D.C. point; wherebythe unburned and partially burned gases are afterburned to a minimum insaid exhaust gas cleaner.
 3. A system for reducing unburned andpartially burned gases contained in engine exhaust gases of an internalcombustion engine of rotary type having an exhaust gas cleaner in itsexhaust system, said system comprising: a bypass conduit having an inletport open into an engine chamber under compression and an outlet portopen into an exhaust system for providing fluid communciationtherebetween, wherein the inlet port of said bypass conduit is locatedin a trailing portion of an engine housing defining said engine chamberfor admitting therethrough an enriched fresh air-fuel mixture leftbehind in the trailing portion of said engine chamber; and control meansresponsive to the compression condition of said engine chamber forperiodically permitting said fluid communication so as to introduce byway of said bypass conduit into said exhaust gas cleaner a freshair-fuel mixture from said engine chamber, whereby the unburned andpartially burned gases are afterburned to a minimum in said exhaust gascleaner.
 4. A system according to claim 2, further comprising shut-offmeans responsive to the operating temperature of said exhaust gascleaner for shutting off the introduction of said fresh air-fuel mixturewhen said operating temperature is above a predetermined level dictatingthat the warming-up of said exhaust gas cleaner is completed.
 5. Asystem according to claim 2, wherein said valve means includes asolenoid valve adapted to open when energized, and a crank angle sensorsensing said crank angle for supplying an electric signal to saidsolenoid valve for its energization when said crank angle reaches saidpredetermined level.
 6. A system according to claim 2, wherein saidvalve means includes a mechanical valve adapted to open when actuated,and a mechanical linkage associated with the rotation of the rotor ofsaid internal combustion engine for actuating said mechanical valve whensaid crank angle reaches said predetermined level.
 7. A system accordingto claim 3, further comprising secondary air means for introducing freshsecondary air into said exhaust system upstream of said exhaust gascleaner in a manner to sufficiently admix said fresh secondary air withsAid engine exhaust gases containing said fresh air-fuel mixture.
 8. Asystem according to claim 7, wherein said secondary air means includes asecondary air conduit having an outlet port open into said exhaustsystem in the vicinity of the outlet port of said bypass conduit, and anair pump having fluid communication with said secondary air conduit forpumping out therethrough said fresh secondary air having a pressurelevel higher than a probable exhaust back pressure in the exhaust portof said internal combustion engine.
 9. A system according to claim 8,wherein said secondary air means further includes an air containermounted between said secondary air conduit and air pump for temporarilystoring said fresh secondary air before its introduction.
 10. A systemaccording to claim 3, further comprising shut-off means responsive tothe operating temperature of said exhaust gas cleaner for shutting offthe introduction of said fresh air-fuel mixture when said operatingtemperature is above a predetermined level dictating that the warming-upof said exhaust gas cleaner is completed.
 11. A system according toclaim 10, wherein said shut-off means includes a shut-off valve mountedsaid bypass conduit in series with said control means and adapted toclose when actuated, and a warming-up sensor sensing the operatingtemperature of said exhaust gas cleaner for actuating said shut-offvalve when said operating temperature is above said predetermined level.12. A system according to claim 11, wherein said warming-up sensor islocated adjacent to an engine housing defining said engine chamber forsensing said operating temperature in terms of the temperature of saidengine housing.
 13. A system according to claim 11, wherein saidwarming-up sensor is located adjacent to said exhaust system for sensingsaid operating temperature in terms of the temperature of said engineexhaust gases.
 14. A system according to claim 11, wherein saidwarming-up sensor is located adjacent to said exhaust gas cleaner forsensing said operating temperature in terms of the temperature of saidexhaust gas cleaner.
 15. A system according to claim 11, wherein saidwarming-up sensor includes a mechanical element mechanically linked withsaid shut-off valve for its actuation.
 16. A system according to claim15, wherein said mechanical element includes a bimetal element forsensing said operating temperature.
 17. A system according to claim 15,wherein said mechanical element includes a thermal expansion element forsensing said operating temperature.
 18. A system according to claim 11,wherein said warming-up sensor includes an electric element forsupplying an electric signal to said shut-off valve for its actuation.19. A system according to claim 18, wherein said electric elementincludes a thermistor for sensing said operating temperature.